Process for the preparation of filled urethane-based reinforced moldings and the resultant products

ABSTRACT

This invention relates to a reaction injection molding process for preparing a molded product by reaction of a mixture of 
     (a) an organic polyisocyanate; 
     (b) one or more compounds containing at least two isocyanate-reactive groups; 
     (c) about 2 to about 20% by weight, based on the weight of the molded product, of rigid fibers having a diameter of from about 5 to about 10 micrometers and a length ranging from the diameter of the fiber up to about 2 millimeters, preferably in admixture with component (b); 
     and, optionally, 
     (d) an inert gas dissolved in at least one of components (a) or (b) in an amount sufficient to produce a molded product having a density of at least 0.80 g/cm 3  ; and 
     (e) up to 15% by weight, based upon the weight of the molded product, of a filler other than rigid fibers (c).

This application is a division of application Ser. No. 08/416,103 filedApr. 4, 1995 now U.S. Pat. No. 5,468,432 which is a continuation of Ser.No. 08/123,318 filed Sep. 17, 1993, now abandoned.

BACKGROUND OF THE INVENTION

This invention relates to a reaction injection molding process forpreparing molded urethane-based products containing rigid fibers havinga diameter of from about 5 to about 10 micrometers as a reinforcingfiller.

The use of fillers in polyurethanes is well known. For example,structural polyurethanes manufactured by reaction injection molding("RIM") typically contain one or more reinforcing fillers. The selectionof the type and quantity of reinforcing fillers in polyurethanesprepared by the RIM process is in general based on the desiredperformance criteria. The addition of fillers to structural partsprovides benefits for a number of reasons, including improved modulus,altered thermal properties such as sag, shrink, and thermal expansion.Fillers are typically added to the isocyanate-reactive component but cansometimes also be added to the isocyanate component as well.

Milled glass fiber has been widely used as a filler for polyurethanes.E.g., U.S. Pat. Nos. 4,381,352, 4,680,214, and 4,861,803. The standardmilled glass fiber used in the polyurethane industry has a diameter ofabout 16 micrometers and nominal lengths referred to as "1/32 inch","1/16 inch", "1/8 inch", or "1/4 inch" (preferably "1/16 inch"). E.g.,S. H. Metzger, Jr. and K. Seel, "High Modulus RIM Elastomers forAutomotive Extedor Body Panels" in J. Cell. Plastics, 268-273 (1981);see also U.S. Pat. No. 4,381,352. The term "nominal length" as used inthe glass industry does not refer to average lengths for a given fibersample but is instead related to the size of a sieve through which thesamples can pass. Within the glass industry, the length of a glass fibercan be expressed in various ways, such as average fiber length or asbulk density. For example, the average length of a "1/16-inch" milledglass fiber is about 0.006 inches (0.15 mm), with the range being fromabout 0.001 inches (0.025 mm) to about 0.04 inches (1.0 mm), and thebulk density of such a fiber is about 0.500 g/cm³.

It has now been found that rigid fiber, particularly milled glass fiber,having a diameter ranging from 5 to 10 micrometers provides unexpectedadvantages when used as a filler for urethane-based products. Forexample, reinforced polyurethanes prepared using milled glass fibershaving a diameter of about 5 to about 10 micrometers exhibit physicalproperties that are equal to or better than reinforced polyurethanescontaining more than twice the quantity of 16 micrometer glass fibers.

SUMMARY OF THE INVENTION

The present invention relates to a reaction injection molding processfor preparing a molded product comprising reacting a mixture of

(a) an organic polyisocyanate;

(b) one or more compounds containing at least two isocyanate-reactivegroups; and

(c) about 2 to about 20% by weight (preferably 4 to 8% by weight), basedon the weight of the molded product, of rigid fibers (preferably milledglass fibers) having a diameter of from about 5 to about 10 micrometers(preferably 7 to 8 micrometers and more preferably 7.5 micrometers) anda length ranging from about the diameter of the fiber up to about 2millimeters (preferably up to 0.5 millimeters), preferably in admixturewith component (b).

The present invention preferably relates to a reaction injection moldingprocess according to the invention in which the reaction mixtureadditionally comprises

(d) an inert gas (preferably air and/or nitrogen gas) dissolved in atleast one of components (a) or (b) in an amount sufficient to produce amolded product having a density of at least about 0.80 g/cm³ (preferably0.85 to 1.10 g/cm³); and

(e) up to about 15% by weight (preferably from 1 to 10% by weight andmost preferably from 4 to 7% by weight), based upon the weight of themolded product, of a filler other than rigid fibers (c) added to atleast one of components (a) or (b) (preferably component (b).

DETAILED DESCRIPTION OF THE INVENTION

Suitable rigid fibers for use as component (c) according to the presentinvention include glass fibers, preferably milled glass fibers, andother essentially incompressible inorganic or organic fibers having adiameter that ranges from about 5 to about 10 micrometers (preferably 7to 8 micrometers and more preferably 7.5 micrometers) and a length thatis at least about equal to the diameter and ranges up to about 2millimeters (preferably up to 0.5 millimeters). Suitable milled glassfibers, for example, can be obtained by hammer milling longer glassfibers prepared, for example, by extruding molten glass throughappropriate dies. Examples of the less preferred inorganic fibersinclude mineral fibers having the appropriate dimensions. Examples ofthe less preferred organic fibers include nylon, aramid, and other suchfibers having the appropriate dimensions. Regardless of whether fibers(c) are milled glass fibers or other materials, they should be both heatresistant and essentially incompressible when subjected to elevatedtemperatures and pressure during the molding process.

It is generally preferred to use rigid fibers to which a liquid sizingagent is applied during or after manufacture of the fiber. Glass fibershaving an organic coating are particularly preferred. E.g., U.S. Pat.Nos. 4,804,771 and 4,849,263.

Suitable polyisocyanates for use as component (a) according to thepresent invention include aliphatic, cycloaliphatic, araliphatic,aromatic and heterocyclic polyisocyanates which are known and described,for example, by W. Siefken in Justus Liebigs Annalen der Chemie, 562,pages 75-136. Specific examples include ethylene diisocyanate;1,4-tetramethylene diisocyanate; 1,6-hexamethylene diisocyanate;1,12-dodecane diisocyanate; cyclobutane-1,3-diisocyanate;cyclohexane-1,3- and -1,4-diisocyanate and mixtures thereof;1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane (isophoronediisocyanate or IPDI); 2,4- and 2,6-hexahydrotoluene diisocyanate andmixtures thereof; hexahydro-1,3- and/or -1,4-phenylene diisocyanate;perhydro-2,4'- and/or -4,4'-diphenylmethane diisocyanate; 1,3- and1,4-phenylene diisocyanate; 2,4- and 2,6-toluene diisocyanate andmixtures thereof; diphenylmethane 2,4'- and/or 4,4'-diisocyanate;naphthylene 1,5-diisocyanate; triphenylmethane-4,4',4"-triisocyanate;and polyphenyl polymethylene polyisocyanates of the type obtained bycondensing aniline with formaldehyde, followed by condensation.

It is preferred to use the readily available polyisocyanates such as2,4- and 2,6-toluene diisocyanate and mixtures of such isomers;polyphenyl polymethylene polyisocyanates of the type obtained bycondensing aniline with formaldehyde, followed by phosgenation; andpolyisocyanates containing carbodiimide groups, urethane groups,allophanate groups, isocyanurate groups, urea groups, or biuret groups.Particularly preferred are the liquid derivatives of4,4'-diphenylmethane diisocyanate (MDI) which may be liquefied byintroducing carbodiimide groups, blending with 2,4'-diphenylmethanediisocyanate or by introducing urethane groups. Especially preferred arethe liquefied derivatives of MDI prepared by reacting MDI with 0.1 to0.3 mols of a polypropylene glycol having a molecular weight of up toabout 700, in particular, dipropylene glycol, tripropylene glycol ormixtures thereof as disclosed, for example, in U.S. Pat. No. 3,644,457.

Also suitable for use as polyisocyanate component (a) areisocyanate-terminated prepolymers based on the above-mentionedpolyisocyanates and the isocyanate-reactive compounds, preferablyhydroxyl compounds, disclosed hereinafter for use in accordance with thepresent invention. Prepolymers of this type are disclosed in U.S. Pat.No. 4,374,210. The prepolymers are preferably based on the polyether orpolyester polyols disclosed hereinafter and, optionally, the lowmolecular weight, hydroxyl group-containing chain extenders which arealso disclosed hereinafter. Blends of any of the previously disclosedpolyisocyanates may also be used in accordance with the presentinvention.

Suitable reactants for preparing the products of the present inventioninclude isocyanate-reactive compounds (b) containing at least twoisocyanate-reactive groups. These compounds may be divided into twogroups, high molecular weight compounds having molecular weights of from400 to about 10,000 and low molecular weight compounds (i.e., chainextenders) having molecular weights of from 62 to 399. Examples ofsuitable high molecular weight compounds include the polyesters,polyethers, polythioethers, polyacetals, and polycarbonates containingat least 2, preferably 2 to 8 and most preferably 2 to 4isocyanate-reactive groups of the type known for the production ofpolyurethanes.

High molecular weight polyethers suitable for use in accordance with theinvention are known and may be obtained, for example, by polymerizingepoxides such as ethylene oxide, propylene oxide, butylene oxide,tetrahydrofuran, styrene oxide, or epichlorohydrin in the presence ofBF₃ or by chemically adding these epoxides, preferably ethylene oxideand propylene oxide, in admixture or successively to componentscontaining reactive hydrogen atoms such as water, alcohols, or amines.Examples of alcohols and amines include the low molecular weight chainextenders set forth hereinafter, 4,4'-dihydroxydiphenylpropane, sucrose,aniline, ammonia, ethanolamine, and ethylene diamine. It is preferred touse polyethers which contain substantial amounts of primary hydroxylgroups in terminal positions (up to 90% by weight, based on all of theterminal hydroxyl groups present in the polyether). Polyethers modifiedby vinyl polymers, of the type formed, for example, by polymerizingstyrene or acrylonitrile in the presence of polyether (U.S. Pat. Nos.3,383,351, 3,304,273, 3,523,093, and 3,110,695; and German Patent1,152,536), are also suitable, as are polybutadienes containing OHgroups.

In addition, polyether polyols that contain high molecular weightpolyadducts or polycondensates in finely dispersed form or in solutionmay be used. Such modified polyether polyols are obtained whenpolyaddition reactions (e.g., reactions between polyisocyanates andamino functional compounds) or polycondensation reactions (e.g., betweenformaldehyde and phenols and/or amines) are directly carried out in situin the polyether polyols.

Suitable examples of high molecular weight polyesters include thereaction products of polyhydric, preferably dihydric alcohols(optionally in the presence of trihydric alcohols), with polyvalent(preferably divalent) carboxylic acids. Instead of using the freecarboxylic acids, it is also possible to use the correspondingpolycarboxylic acid anhydrides or corresponding polycarboxylic addesters of lower alcohols or mixtures thereof for producing thepolyesters. The polycarboxylic acids may be aliphatic, cycloaliphatic,aromatic, and/or heterocyclic and may be unsaturated or substituted (forexample, by halogen atoms). The polycarboxylic adds and polyols used toprepare the polyesters are known and described, for example, in U.S.Pat. Nos. 4,098,731 and 3,726,952, herein incorporated by reference intheir entirety. Suitable polythioethers, polyacetals, polycarbonates,and other polyhydroxyl compounds are also disclosed in theabove-identified U.S. patents. Finally, representatives of the many andvaried compounds which may be used in accordance with the invention maybe found for example in High Polymers, Volume XVI, "Polyurethanes,Chemistry and Technology," by Saunders and Frisch, IntersciencePublishers. New York, London, Vol. 1, 1962, pages 32-42 and 44-54. andVolume II. 1964, pages 5-6 and 198-199; and in Kunststoff-Handbuch, Vol.VII, Vieweg-Hochtlen, Cad Hanser Verlag, Munich, 1966, pages 45-71.

Suitable aminopolyethers which may be used in accordance with thepresent invention as high molecular weight compounds (the molecularweight always being the average molecular weight which may be calculatedfrom the functionality and the content of isocyanate-reactive groups)are those in which at least about 30 and preferably about 60 to 100equivalent percent of the isocyanate-reactive groups are primary and/orsecondary (preferably primary) aromatically or aliphatically (preferablyaromatically) bound amino groups and the remainder are primary and/orsecondary aliphatically bound hydroxyl groups.

In these compounds, the terminal residues carrying the amino groups mayalso be attached to the polyether chain by urethane or ester groups.These "aminopolyethers" are prepared by known methods. For example,polyhydroxypolyethers such as polypropylene glycol ethers may beaminated by reaction with ammonia in the presence of Raney nickel andhydrogen (Belgian Patent 634,741). U.S. Pat. No. 3,654,370 describes theproduction of polyoxyalkylene polyamines by reaction of thecorresponding polyol with ammonia and hydrogen in the presence of anickel, copper, or chromium catalyst. German Patent 1,193,671 describesthe production of polyethers containing terminal amino groups byhydrogenation of cyanoethylated polyoxypropylene ethers. Other methodsfor the production of polyoxyalkylene (polyether) amines are describedin U.S. Pat. Nos. 3,155,728 and 3,236,895 and in French Patent1,551,605. The production of polyethers containing terminal secondaryamino groups is described, for example, in French Patent 1,466,708.

Polyhydroxypolyethers of relatively high molecular weight may beconverted into the corresponding anthranilic acid esters by reactionwith isatoic acid anhydride, as described, for example, in GermanOffenlegungsschriften 2,019,432 and 2,619,840 and in U.S. Pat. Nos.3,808,250, 3,975,428, and 4,016,143. Polyethers containing terminalaromatic amino groups are formed in this way.

According to German Offenlegungsschrift 2,546,536 and U.S. Pat. No.3,865,791, relatively high molecular weight compounds containingterminal amino groups are obtained by reaction of NCO prepolymers basedon polyhydroxypolyethers with enamines, aldimines, or ketiminescontaining hydroxyl groups and subsequent hydrolysis.

It is preferred to use amino polyethers obtained by hydrolysis ofcompounds containing terminal isocyanate groups, for example, inaccordance with German Offenlegungsschdft 2,948,419 or U.S. Pat. No.4,515,923, herein incorporated by reference in its entirety. In thisprocess, polyethers most preferably containing 2 to 4 hydroxyl groupsare allowed to react with polyisocyanates to form NCO prepolymers and,in a second step, the isocyanate groups are converted by hydrolysis intoamino groups.

The aminopolyethers used in accordance with the invention are oftenmixtures of the compounds mentioned by way of example and (on astatistical average) most preferably contain 2 to 4 terminalisocyanate-reactive groups. In the process according to the invention,the aminopolyethers may be used in admixture with polyhydroxypolyethersfree from amino groups.

In accordance with the present invention, the high molecular weightcompounds are used in admixture with up to about 95% by weight(preferably up to about 50% by weight, more preferably about 8 to 30% byweight, and most preferably about 12 to 26% by weight), based on thetotal quantity of the high molecular weight compounds, of the lowmolecular weight chain extenders. Examples of suitable hydroxylgroup-containing chain extenders include ethylene glycol, 1,2- and1,3-propanediol, 1,3- and 1,4- and 2,3-butanediol, 1,6-hexanediol,1,10-decanediol, diethylene glycol, triethylene glycol, tetraethyleneglycol, dipropylene glycol, tripropylene glycol, glycerol, andtrimethylolpropane.

Other suitable chain extenders include aromatic polyamines (preferablydiamines) having molecular weights of less than 400, especially thesterically hindered aromatic polyamines (preferably diamines) havingmolecular weights of less than 400, especially the sterically hinderedaromatic aliamines which contain at least one linear or branched alkylsubstituent in the ortho-position to the first amino group and at leastone (preferably two) linear or branched alkyl substituents containingfrom 1 to 4 (preferably 1 to 3) carbon atoms in the ortho-position to asecond amino group. These aromatic diamines include1-methyl-3,5-diethyl-2,4-diaminobenzene,1-methyl-3,5-diethyl-2,6-diaminobenzene,1,3,5-trimethyl-2,4-diaminobenzene, 1,3,5-triethyl-2,4-diaminobenzene,3,5,3',5'-tetraethyl-4,4'-diaminodiphenylmethane,3,5,3',5'-tetraisopropyl-4,4'-diaminodiphenyimethane,3,5-diethyl-3',5'-diisopropyl-4,4'-diaminodiphenylmethane,3,5-diethyl-5,5'-diisopropyl-4,4'-diaminodiphenylmethane,1-methyl-2,6-diamino-3-isopropylbenzene, and mixtures of the abovealiamines. Most preferred are mixtures of1-methyl-3,5-diethyl-2,4-diaminobenzene and1-methyl-3,5-diethyl-2,6-diaminobenzene in a weight ratio between about50:50 to 85:15 (preferably about 65:35 to 80:20).

In addition, aromatic polyamines may be used in admixture with thesterically hindered chain extenders and include, for example, 2,4-and2,6-diaminotoluene, 2,4'- and/or 4,4'-diaminodiphenylmethane, 1,2- and1,4-phenylenediamine, naphthalene-1,5-diamine andtriphenyimethane-4,4',4"-triamine. The difunctional and polyfunctionalaromatic amine compounds may also exclusively or partly containsecondary amino groups such as 4,4'-di(methylamino)diphenylmethane or1-methyl-2-methylamino-4-aminobenzene. Liquid mixtures of polyphenylpolymethylene-polyamines, of the type obtained by condensing anilinewith formaldehyde, are also suitable. Generally, the nonstericallyhindered aromatic diamines and polyamines are too reactive to providesufficient processing time in a RIM system. Accordingly, these diaminesand polyamines should generally be used in combination with one or moreof the previously mentioned sterically hindered diamines or hydroxylgroup-containing chain extenders.

In a preferred embodiment of the invention, which is particularlysuitable for preparing low-density products, an inert gas (d) isintroduced into one or more of the reactive components (preferably intocomponent (b)) using techniques known in the art. As used herein, theterm "inert gas" refers to gaseous materials that are essentiallyunreactive under the conditions used in the process of the invention.Examples of suitable inert gases include air, nitrogen, argon, carbondioxide, or mixtures thereof. When preparing the preferred low densityproducts, the inert gas is introduced in sufficient quantity to giveproducts having a density of at least about 0.80 g/cm³ (preferablyranging from 0.85 to 1.10 g/cm³).

The inert gas is preferably introduced using commercial equipment, suchas Diffuser Stone-KIMEX mixers and venturi type mixers. The presentlypreferred device is a Hennecke Aeromat-GU which is described in HenneckeTrade Bulletin #41 and in a 1991 article entitled "ConsistentDistribution of Finely Dispersed Gases in Polyol Streams", Proksa et al,in Polyurethanes World Congress 1991. Sufficient inert gas iscustomarily introduced into the system in an amount in excess of theamount necessary to saturate the particular component at a feed tankpressure of from about 0.21 to about 0.35 N/mm². As is known in the art,material flows from the feed tank through a transfer pump (whichincreases the pressure of the particular component) through a meteringpump to the mixhead. Discharge pressures of the transfer pump aregenerally in the range of 0.35 to 0.7 N/mm², while discharge pressuresof the metering pump are generally in the range of 14 to 21 N/mm². Theamount of the gas in the system is generally monitored using commercialmeasuring equipment which responds to changes in specific gravity of theliquid components. One such device is the Dynatrol (manufactured byAutomation Products), which permits the effective control of the gascontent by monitoring any changes in the specific gravity of the liquidcomponent.

When preparing low density products, factors that are important toachieving high quality low density product include enhanced flowcharacteristics and reduced nucleation density of theisocyanate-reactive component. Good flow properties are importantbecause relatively smaller quantities of reactive materials are requiredfor low density products. Reduced nucleation density is directly relatedto an increased amount of inert gas dissolved or dispersed in theisocyanate-reactive component and ultimately to a lower density product.The use of rigid microspheres according to the present invention hasbeen found to be particularly useful in enhancing both the flowcharacteristics and the nucleation density of the isocyanate-reactivecomponent, as well as reducing the time required to achieve a givennucleation density. As a result, a significant reduction in density forthe molded parts is achieved while at the same time improving demoldcharacteristics (such as mold release, green strength, and hot tearstrength) without adversely affecting physical properties. In fact,impact resistance is consistently improved. The use of hollow ratherthan solid microspheres provides an even further reduction in density,while still providing improved physical properties and demoldcharacteristics, and is thus particularly preferred.

In a preferred embodiment, up to about 15% by weight, relative to therigid fibers (c), of additional fillers (e) are also included in thereaction mixture. Suitable fillers include reinforcement fillers andother types of fillers known in the art for use with urethane-basedproducts. Reinforcement fillers that allow reduced contraction of themolded product upon cooling, as well as adjustment of tensile modulusand flex modulus, are well known in the art. Suitable inorganicreinforcement fillers include glass in the form of fibers (other thanfibers having the characteristics specified for component (c)) orflakes, mica, wollastonite, carbon black, talc, calcium carbonate, andcarbon fibers. Organic fillers, although less preferred, are alsosuitable for reinforcement.

Particularly preferred additional fillers (e) include rigid andcompressible microspheres.

Suitable rigid microspheres for use as an additional filler (e)according to the invention can be hollow microspheres (also known asmicroballoons or microbubbles) or solid microspheres. When preparinglow-density materials, for example, hollow spheres are generallypreferred. However, regardless of whether the microspheres are hollow orsolid, they should be heat resistant and essentially incompressible whensubjected to elevated temperatures and pressure during the moldingprocess. In a typical RIM process, compression strengths greater thanabout 12 mPa.s (preferably greater than 20 mPa.s) are generallysuitable. With hollow microspheres, wall thickness is, of course, aselection factor. Suitably rigid microspheres may be made of inorganicmaterials, such as glass, ceramic, and carbon, or rigid organicpolymers, such as phenolic resins. Solid microspheres can be prepared byany of several methods known in the art. For example, solid microspherescan be prepared by softening irregularly shaped particles just enoughfor then to flow into spheres under the influence of surface tension, byquenching a melt in a cooler medium, or by carrying out polymerizationsin well-stirred suspensions at elevated temperature. Hollow inorganicmicrospheres can be prepared by several known methods, For example,hollow glass spheres can be prepared by grinding and sizing soda-limeglass cullet to form particles that, in combination with blowing agents,are passed through a gas flame (ca. 1000° C.) to soften the glass andgenerates gases that expand the particles. See U.S. Pat. No. 3,365,315.Hollow glass spheres can also be prepared by spray-drying a sodiumborosilicate solution containing a blowing agent to form a particulatematerial that is passed through a gas flame to form the spheres. SeeU.S. Pat. No. 2,978,339. Ceramic microspheres can be obtained as bothsolid and hollow microspheres as a normal aluminosilicate by-product ofburning coal. In general, hollow ceramic microspheres are heavier thansimilarly sized glass microspheres. Although inorganic microspheres canbe treated with a silane or titanate coupling agent to enhance adhesionwith the matrix urethane polymer, the untreated particles generallyexhibit sufficient adhesion to the polymer, making such treatmentsunnecessary. Commercially available hollow inorganic microspheresinclude ceramic Z-Light Spheres and glass Scotchlite K46 Glass Bubblesfrom 3M Company. Commercially available glass microspheres typicallycontain about 72 wt. % SiO₂, 14 wt. % Na₂ O, 10 wt. % CaO, 3 wt. % MgO,and 1 wt. % Al₂ O₃ /K₂ O/Li₂ O, whereas commercially available ceramicmicrospheres typically contain about 50-58 wt. % SiO₂, 25-30 wt. % Al₂O₃, 6-10 wt. % CaO, 1-4 wt. % Na₂ O/K₂ O, and 1-5 wt. % other oxides.E.g., J. F. Plummer, "Microspheres" in Encyclopedia of Polymer Scienceand Technology, Vol. 9 (John Wiley & Sons. Inc., 1987). page 788. Solidmicrospheres of organic polymers can be prepared using aqueousdispersions of suitable film-forming thermoset or thermoplasticmaterials. In the presence of a blowing agent, this method gives hollowmicrospheres. It is typical of available rigid microspheres that a givensample contains a range of sizes. Suitable microspheres for the presentinvention typically have a diameter of between about 1 and about 350 Nm(preferably 10 to 210 μm. The specific size range however, is oftendependent on the selection of particular injection equipment andoperating parameters (for example, nozzle diameter). Low density(especially hollow) microspheres are preferred, with those havingdensities ranging from 0.05 to 2.5 g/cm³ being particularly preferred.The rigid microspheres can be added to either the isocyanate componentor the isocyanate-reactive component, although addition toisocyanate-reactive component (b) is preferred.

Although less preferred, it is also possible to include knowncompressible expanded microspheres, such as those described in U.S. Pat.Nos. 4,038,238, 4,829,094, 4,843,104, 4,902,722 and 4,959,395, andJapanese Patent Publication 60-244511. Commercially availablecompressible microspheres include Dualite M6017AE, Dualite M6001AE, andDualite M6029AE, all available from Pierce & Stevens Corporation, andExpancel available from Nobel Industries. These commercially availablecompressible microspheres are expanded, hollow microspheres consistingof a thin shell of a vinylidene chloride, polypropylene, oracrylonitrile copolymer. The interior of the Dualite and Expancelmicrospheres contains a volatile liquid, such as a low-boilinghydrocarbon (which is pentane for Dualite microspheres and isobutane forExpancel microspheres), which is used to expand the microsphere andremains inside the shell thereafter. An organic or inorganic materialthat decomposes upon only moderate heating will also serve to expand themicrosphere, with the decomposition products remaining in the shellthereafter. Also present on the outside of Dualite microspheres is arough coating of calcium carbonate dust.

It is also possible to use compressible microspheres in combination withrigid microspheres, but the amount of compressible microspheres shouldpreferably not exceed 50% by weight of the amount of the rigidmicrospheres.

Additives which may be used in the present invention include catalysts,especially tin(11) salts of carboxylic acids, dialkyltin salts ofcarboxylic acids, dialkyltin mercaptides, dialkyltin dithioesters, andtertiary amines. Preferred among these catalysts are dibutyltindilaurate and 1,4-diazabicyclo[2,2,2]octane (triethylene diamine),especially mixtures of these catalysts. The catalysts are generally usedin amounts of about 0.01 to 10% (preferably about 0.05 to 2%), based onthe weight of the high molecular weight component.

It is also possible to use surface-active agents such as emulsifiers andfoam stabilizers. Examples include siloxanes,N-stearyl-N',N'-bis-hydroxyethyl urea, oleyl polyoxyethylene amide,stearyl diethanoiamide, isostearyl diethanolamide, polyoxyethyleneglycol monoleate, a pentaerythritol/adipic acid/oleic acid ester, ahydroxyethyl imidazole derivative of oleic acid, N-stearyl propylenediamine, and the sodium salts of castor oil sulfonates or of fattyacids. Alkali metal or ammonium salts of sulfonic acid, such asdodecylbenzenesulfonic acid or dinaphthylmethanesuifonic acid, and fattyacids may also be used as surface-active additives. Particularlysuitable surface-active compounds include polyether siloxanes of thetype generally known for use in the polyurethane art, such aswater-soluble polyether siloxanes. The structure of these siloxanes isgenerally such that a copolymer of ethylene oxide and propylene oxide isattached to a polydimethylsiloxane functionality. Methods ofmanufacturing preferred siloxanes are described in U.S. Pat. No.4,906,721, the disclosure of which is herein incorporated by reference.

It is also possible to use mold release agents, which are compounds thatare added to the reactive components of the isocyanate additionreaction, usually the isocyanate-reactive component, to assist in theremoval of a polyurethane product from a mold. Suitable mold releaseagents for the present invention include those based at least in pad onfatty add esters (e.g., U.S. Pat. Nos. 3,726,952, 3,925,527, 4,058,492,4,098,731, 4,201,847, 4,254,228, 4,868,224, and 4,954,537 and BritishPatent 1,365,215); metal and/or amine salts of carboxylic acids, amidocarboxylic acids, phosphorus-containing acids, or boron-containing acids(e.g., U.S. Pat. Nos. 4,519,965, 4,581,386, 4,585,803, 4,876,019,4,895,879, and 5,135,962); polysiloxanes (e.g., U.S. Pat. No.4,504,313); amidines (e.g., U.S. Pat. Nos. 4,764,540, 4,789,688, and4,847,307); resins prepared by the reaction of isocyanate prepolymersand a polyaminepolyimine component (e.g., U.S. Pat. No. 5,198,508); andneutralized esters prepared from certain amine-started tetrahydroxycompounds described in U.S. Pat. No. 5,208,268. Particularly preferredmold release agents contain zinc stearate.

In addition to the additional fillers, catalysts, surface-active agents,and mold release agents mentioned above, other additives which may beused in the molding compositions of the present invention includeblowing agents, cell regulators, flame retarding agents, plasticizers,and dyes of the types generally known in the art.

The compositions according to the present invention are especiallysuited for processing by the RIM process. In general, two separatestreams are intimately mixed and subsequently injected into a suitablemold, although it is possible to use more than two streams. In apreferred embodiment, the first stream contains the polyisocyanatecomponent, whereas the second stream contains the isocyanate-reactivecomponent, chain extender, rigid fibers and other fillers, any internalmold release agent, and any other additives which are to be included.Although generally less preferred, it is, of course, also possible toadd the rigid fibers and/or other fillers to the polyisocyanatecomponent. Regardless of which reactive component contains the rigidfillers and/or other fillers, it is generally necessary to maintainhomogeneity by agitation.

The quantity of polyisocyanate used in the process according to thepresent invention is preferably calculated so that the foamable mixturehas an isocyanate index of from 70 to 130 (preferably from 90 to 110).By "isocyanate index" is meant the quotient of the number of isocyanategroups and number of groups which are reactive with isocyanates,multiplied by 100.

The known RIM process is used for carrying out the process according tothe present invention. In general, the components may be mixedsimultaneously, or the non-reactive components may be pre-mixed and thenmixed with the reactive components. A starting temperature of from 10°to 70° C. (preferably from 30° to 50° C.) is generally chosen for themixture introduced into the mold. The temperature of the mold itself isgenerally from 40° to 100° C. (preferably from 50° to 70° C.). Aftercompletion of the reaction and molding process, the resultant product isremoved from the mold.

The moldings obtainable by the process according to the presentinvention are particularly suitable for the manufacture of a variety ofpolyurethane products. For example, in a preferred embodiment of theinvention, low density products such as flexible car bumpers and carbody elements can be produced. With suitable variation of the startingcomponents, it is also possible to produce materials which have goodabrasion resistance and high mechanical strength, such as flexiblepolyurethane shoe soles.

The following examples further illustrate details for the process ofthis invention. The invention, which is set forth in the foregoingdisclosure, is not to be limited either in spirit or scope by theseexamples. Those skilled in the art will readily understand that knownvariations of the conditions of the following procedures can be used,Unless otherwise noted, all temperatures are degrees Celsius and allparts and percentages are parts by weight and percentages by weight,respectively.

EXAMPLES Example 1

An isocyanate-reactive blend was prepared using 76.8 parts of atrifunctional polyether polyol having a molecular weight of 6000(glycerol started using propylene oxide and ethylene oxide at a weightratio of about 5:1); 16 parts of diethyltoluene aliamine ("DETDA"); 7parts of a zinc stearate concentrate containing 3 parts of a diaminehaving a molecular weight of 400 available as JEFFAMINE® D-400 fromTexaco, 2 parts of zinc stearate, and 2 parts of a tetrafunctionalpolyol having a molecular weight of 356 prepared from ethylene diamineand propylene oxide; 0.1 parts of triethyleneamine (available as DABCO®33-LV from Air Products and Chemicals, Inc.); 0.05 parts of dibutyltindilaurate (available as DABCO®T-12 from Air Products and Chemicals,Inc.); and 0.05 parts of dimethyltin dilaurate (available as FORMEZ®UL-28 from Witco Corporation).

A slurry based on this isocyanate-reactive blend was prepared forreinforced reaction injection molding ("RRIM") by adding 13 parts of amilled glass fiber having a diameter of 7.5 μm and a nominal length of"1/16 inch" (i.e., actual length range of about 7-500 μm) (available as742-A from Owens Corning) per 100 parts of the isocyanate-reactiveblend. The isocyanate-reactive slurry was charged to the polyol run tankof a Hennecke LK-06 RRIM machine and nucleated by introduction ofnitrogen gas using a hollow-shaft high-speed cavitation-type nucleatoruntil a nucleation density level of 0.72 g/cm³ was obtained.

The isocyanate-reactive slurry was allowed to react with an isocyanateprepared from 4,4'-diphenylmethane diisocyanate and tripropylene glycoland having an NCO content of about 22.5% using 47 parts of isocyanateper 100 parts of slurry. Urethane parts were molded using the HenneckeLK-06 RRIM machine using a steel mold (P-2 steel) having the dimensionsof 3 mm×20 cm×30 cm. The reactant temperatures were 43° to 46° C. forthe isocyanate and 52° to 57° C. for the isocyanate-reactive slurry, andthe mixing pressure for both components was 20 mPa.s. Physicalproperties of the resultant polyurethane are shown in Table 1.

Example 2 (Comparison)

A isocyanate-reactive slurry was prepared according to Example 1 exceptfor using 27 parts of milled glass fibers having a larger diameter of 16μm and a nominal length of "1/16 inch" (available as 737-BD from OwensCorning) per 100 parts of the isocyanate-reactive blend. Theisocyanate-reactive slurry was charged to the polyol run tank of aHennecke LK-06 RRIM machine and nucleated as in Example 1 until anucleation density level of 0.77 g/cm³ was obtained.

The isocyanate-reactive slurry was allowed to react with the sameisocyanate as used in Example 1 using 42 parts of isocyanate per 100parts of slurry. Urethane parts were molded as in Example 1. Physicalproperties of the resultant polyurethane are shown in Table 1.

                  TABLE 1                                                         ______________________________________                                        Physical properties for Example 1 and comparison Example 2.                                      Example                                                                       1    2                                                     ______________________________________                                        Density (g/cm.sup.3) 1.05   1.10                                              Flexural modulus (mPa · s)                                                                495    428                                               Tensile strength (mPa · s)                                                                18.3   14.1                                              Elongation (%)       145    135                                               Tear strength (N/mm) 84.9   72.3                                              Heat sag (mm).sup.(1)                                                                              6.5    8.9                                               Shrink (%)           0.39   0.71                                              ______________________________________                                         .sup.(1) Heat sag using 15cm overhang at 250° C. for one hour.    

Despite the use of a smaller quantity of glass fiber, the filledpolyurethane of Example 1 containing milled 7.5-pro diameter glass fiberexhibits physical properties that match or exceed those of thepolyurethane of comparison Example 2 containing a standard 16-μmdiameter glass fiber.

Example 3

Example 1 was repeated except for using a different isocyanate-reactiveblend prepared using 72.25 parts of the trifunctional polyether polyolused in Example 1; 19 parts of DETDA; 8 parts of a zinc stearateconcentrate containing 4 parts of the diamine used in Example 1, 2 partsof zinc stearate, and 2 parts of the tetrafunctional polyol used inExample 1; 0.1 parts of triethyleneamine; 0.05 parts of dibutyltindilaurate; 0.1 parts of dimethyltin dilaurate; and 0.5 parts of apolysiloxane available as TEGOSTAB® B-8481 from Goldschmidt.

A slurry based on this isocyanate-reactive blend was prepared forreinforced reaction injection molding by adding 14 parts of the milled7.5-μm diameter glass fiber used in Example 1 and 1.7 parts of DUALITE®M-6017-AE microspheres (available from Pierce & Stevens Corporation) per100 parts of the isocyanate-reactive blend. The isocyanate-reactiveslurry was charged to the polyol run tank of a Cincinnati Milacron CM-90RRIM machine and nucleated by introduction of nitrogen gas as in Example1 until a nucleation density level of 0.65 g/cm³ was obtained.

The isocyanate-reactive slurry was allowed to react with the sameisocyanate as used in Example 1 using 50 parts of isocyanate per 100parts of slurry. Urethane parts were molded using the CincinnatiMilacron CM-90 RRIM machine using a steel mold (P-2 steel) having thedimensions of 4.5 mm×64 cm×92 cm. The reactant temperatures were 43° to46° C. for the isocyanate and 52° to 57° C. for the isocyanate-reactiveslurry, and the mixing pressure for both components was 11.2 mPa.s.Physical properties of the resultant polyurethane are shown in Table 2.

Example 4

Example 1 was repeated except for using a different isocyanate-reactiveblend prepared using 74.25 parts of the trifunctional polyether polyolused in Example 1; 17 parts of DETDA; 8 parts of the zinc stearateconcentrate used in Example 3; 0.1 parts of triethyleneamine; 0.05 partsof dibutyltin dilaurate; 0.1 parts of dimethyltin dilaurate; and 0.5parts of the polysiloxane used in Example 3.

A slurry based on this isocyanate-reactive blend was prepared forreinforced reaction injection molding by adding 14 parts of the milled7.5-μm diameter glass fiber used in Example 1 and 7.8 parts of ceramicZ-Light Spheres (available from 3M Company) per 100 parts of theisocyanate-reactive blend. The isocyanate-reactive slurry was charged tothe polyol run tank of a Cincinnati Milacron CM-90 RRIM machine andnucleated as in Example 1 until a nucleation density level of 0.63 g/cm³was obtained.

The isocyanate-reactive slurry was allowed to react with the sameisocyanate as used in Example 1 using 45 parts of isocyanate per 100parts of slurry. Urethane parts were molded as in Example 3. Physicalproperties of the resultant polyurethane are shown in Table 2.

                  TABLE 2                                                         ______________________________________                                        Physical properties for Examples 3 and 4.                                                        Example                                                                       3    4                                                     ______________________________________                                        Density (g/cm.sup.3) 0.96   0.97                                              Flexural modulus (mPa · s)                                                                438    379                                               Tensile strength (mPa · s)                                                                15.8   14.9                                              Elongation (%)       81     70                                                Tear strength (N/mm) 74.9   70.0                                              Heat sag (mm).sup.(1)                                                                              13.0   17.0                                              ______________________________________                                         .sup.(1) Heat sag using 15 cm overhang at 250° C. for one hour.   

What is claimed is:
 1. A molded product prepared by a reaction injectionmolding process comprising reacting(a) an organic polyisocyanate with amixture consisting essentially of (b) one or more compounds containingat least two isocyanate-reactive groups; (c) 2 to 20% by weight, basedon the weight of the molded product, of rigid fibers having a diameterof from 7 to 10 micrometers and a length ranging from the diameter ofthe fiber up to 2 millimeters; (d) optionally, an inert gas dissolved incomponent (b) in an amount sufficient to produce a molded product havinga density of at least 0.80 g/cm³ ; (e) 0 to 15% by weight, based uponthe weight of the molded product, of a filler other than rigid fibersadded to component (b); and (f) optionally, a mold release agent.
 2. Amolded product according to claim 1 wherein rigid fibers (c) are milledglass fibers.
 3. A molded product according to claim 2 wherein themilled glass fibers have a diameter of 7 to 8 micrometers.
 4. A moldedproduct according to claim 2 wherein the milled glass fibers have adiameter of 7.5 micrometers.
 5. A molded product according to claim 2wherein the milled glass fibers are present in an amount of from 4 to 8%by weight, based upon the amount of the molded product.
 6. A moldedproduct according to claim 1 wherein inert gas (d) is air and/ornitrogen gas.
 7. A molded product according to claim 1 wherein inert gas(d) is dissolved in component (b) in an amount sufficient to produce amolded product having a density of 0.85 to 1.10 g/cm³.
 8. A moldedproduct according to claim 1 wherein filler (e) is used in an amount offrom 1 to 10% by weight based upon the weight of the molded product. 9.A molded product according to claim 1 wherein filler (e) is selectedfrom the group consisting of rigid microspheres, compressiblemicrospheres, mica, wollastonite, carbon black, talc, calcium carbonate,and carbon fibers.
 10. A molded product according to claim 1 whereinmold release agent (f) comprises zinc stearate.